Repairing bad areas in mesh
All of your issues are the result of the same problem: the subsurf modifier will give you unpredictable, and mostly ugly, results when using ngons (polygons with more than 4 vertices).

1 Delete this Ngon and reconnect the vertices forming quads.



2 Other ngon... add loop cuts to keep the topology consistent using quads.



3 Yet another ngon!:



4 You have vertices that are going past the axis of symmetry used by the mirror modifier. That's bound to cause you more errors down the line.

Scale them to 0 in the Z axis (SZ0)